Treatment of influenza

ABSTRACT

The present invention provides a double-stranded RNA which inhibits replication of influenza B viruses by RNA interference, in which the double-stranded RNA comprises an RNA having 19 to 25 nucleotides homologous with a part of an mRNA transcribed from a genomic RNA of the influenza B viruses and an antisense RNA thereof.

TECHNICAL FIELD

The present invention relates to a double-stranded RNA, hairpin RNA, anda vector, as well as a pharmaceutical composition, an anti-influenzavirus agent, and a detection kit for influenza B viruses containing thedouble-stranded RNA, the hairpin RNA, and the vector.

BACKGROUND ART

Influenza is one of the infectious diseases most widely spread all overthe world, and 250,000 to 500,000 people die of the disease annually. InJapan, 5 to 15% of the population contract influenza annually, and thereare cases in which aged individuals or immunocompromised patients whohave contracted influenza are complicated with pneumonia and result indeath.

Influenza viruses are classified into three groups, namely type A, typeB, and type C, based on differences in the antigenicity of protein whichconstructs a virus particle. Among them, type A and type B are mainlythe ones which cause an infection in humans and circulate repeatedlyevery winter.

Influenza vaccines are used to prevent influenza.

Attenuated live vaccines (i.e., in which attenuated viable pathogens areemployed), inactivated vaccines (i.e., in which pathogens which lostinfectivity after being subjected to inactivation treatment areemployed), and component vaccines (i.e., in which purified specificcomponents of pathogens are employed) are used worldwide, among whichonly component vaccines are practically used in Japan for prevention ofinfluenza viruses.

A strain which is likely to prevail in a current year is predicted basedon information of the influenza virus strain which circulated in theprevious season, genetic information of the influenza virusesconcurrently isolated in other countries, the prevalence of antibody foran influenza virus strain in the population, and the like, and influenzavaccines are produced based on the prediction.

Treatment methods of influenza include pharmacotherapy using ananti-influenza virus agent, and amantadine and a neuraminidase inhibitor(i.e., oseltamivir and zanamivir) are approved as anti-influenza virusagents in Japan (Non-Patent Document 1).

Meanwhile, RNAi (i.e., abbreviation of RNA interference) was found as ameans for inhibiting expression of a specific gene in recent years. RNAinterference refers to a biological phenomenon of inhibition ofexpression of a target gene, in which an mRNA, which is a transcriptionproduct of a target gene, is specially cleaved by a double-stranded RNAhomologous with a specific region of the target gene at a sitehomologous with the double-stranded RNA (Patent Document 1).

In mammalian cells, introduction of a long-chain double-stranded RNAinto a cell induces interferon and causes apoptosis. However, it hasbeen elucidated that an mRNA of a target gene is specifically cleavedwithout causing apoptosis and thus a function of the target gene can beinhibited by introduction of a short-chain double-stranded RNA having 21to 23 by into a cell (Patent Document 2). Here, a short-chaindouble-stranded RNA which causes RNA interference in mammalian cells iscalled siRNA (i.e., abbreviation of small interfering RNA).

Patent Document 1: WO1999/32619 Patent Document 2: WO2001/075164Non-Patent Document 1: Norio SUGAYA, Japanese Journal of ClinicalMedicine, 2006, vol. 64, p. 1840-1844 DISCLOSURE OF THE INVENTIONProblems to be Solved by the Invention

However, accurate prediction of an epidemic strain of influenza virusesis extremely difficult, and the current situation is that whenprediction of an epidemic strain is missed, an effect of an influenzavaccine is markedly reduced.

In addition, even if prediction of an epidemic strain comes true, thereare cases in which side effects such as pyrexia, rash, convulsion,anaphylactic shock, and hepatic function disorder develop withadministration of an influenza vaccine, and they are fatal in aworst-case scenario.

Furthermore, amantadine is an anti-influenza virus agent which targetsM2 protein of influenza A viruses, therefore, it is ineffective forinfluenza B viruses which do not have M2 protein. Meanwhile, aneuraminidase inhibitor is subtly effective for influenza B viruses,whilst it poses a problem of serious side effects. In sum, there is noeffective treatment method for influenza B viruses compared withinfluenza A viruses in the current situation.

In view of the foregoing, an object of the present invention is to treatand prevent an infection caused by influenza B viruses by inhibitingreplication of a wide range of influenza B virus strains.

Means for Solving the Problems

In order to achieve the object, the present invention provides adouble-stranded RNA which inhibits replication of influenza B viruses byRNA interference, in which the double-stranded RNA comprises an RNAhaving 19 to 25 nucleotides homologous with a part of an mRNAtranscribed from a genomic RNA of influenza B viruses and an antisenseRNA thereof.

The present inventors found that double-stranded RNA comprising RNAhaving 19 to 25 nucleotides homologous with a part of an mRNAtranscribed from a genomic RNA of influenza B viruses and an antisenseRNA thereof inhibited replication of influenza B viruses, and furtherfound that an infection caused by influenza B viruses could beeffectively treated and prevented by introducing the double-stranded RNAinto mammalian cells.

The mRNA is preferably a mRNA of an NP protein gene, an RNA polymerasePA subunit gene, an RNA polymerase PB1 subunit gene, or an RNApolymerase PB2 subunit gene.

By introducing a double-stranded RNA comprising RNA having 19 to 25nucleotides homologous with a part of an mRNA transcribed from an NPprotein gene, an RNA polymerase PA subunit gene, an RNA polymerase PB1subunit gene, or an RNA polymerase PB2 subunit gene and antisense RNAthereof into a cell, an mRNA expressed by transcription of these genesis specifically cleaved by RNA interference, thereby replication ofinfluenza B viruses can be inhibited.

The RNA is preferably selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or selectedfrom the group consisting of RNA of nucleotide sequences as set forth inSEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted.Among them, it is more preferably selected from the group consisting ofRNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 11 orselected from the group consisting of RNA of nucleotide sequences as setforth in SEQ ID NOs: 1 to 11 in which 1 to 3 nucleotide(s) is/aresubstituted.

Introduction of double-stranded RNA consisting of any one of RNA havinga nucleotide sequence as set forth in SEQ ID NOs: 1 to 57 and antisenseRNA thereof into a cell can inhibit replication of influenza B virusesmore strongly by RNA interference. Also, introduction of double-strandedRNA consisting of any one of RNA having a nucleotide sequence as setforth in SEQ ID NOs: 1 to 11 and antisense RNA thereof into a cell caninhibit replication of a much wider range of influenza B virus strains.

The double-stranded RNA preferably has a S/N ratio of 3 or greater inscreening of double-stranded RNA by a transfection microarray usingB/Johannesburg/5/99 strain.

A double-stranded RNA having a S/N ratio of 3 or greater can cleave mRNAmore specifically by RNA interference.

The RNA can contain one or more modified ribonucleotide(s), and a 2′-OHgroup of a ribose ring is preferably substituted with a fluoro group, amethyl group, a methoxyethyl group, or a propyl group in the modifiedribonucleotides. Also, one or more phosphodiester bond(s) in the RNA canbe substituted with phosphorothioate bond(s).

RNA introduced into a cell can be degraded by intracellularribonucleases, however, an RNA chain modified as above gains resistanceto the ribonucleases and therefore can efficiently exert an RNAinterference activity.

The double-stranded RNA can form blunt ends, however, it preferablyforms overhanging ends by having DNA or RNA of 1 to 4 nucleotide(s)attached to 3′ ends of a sense and an antisense strands thereof.

A Double-stranded RNA forming overhanging ends has a stronger RNAinterference activity so that it can inhibit replication of influenza Bviruses more remarkably.

In addition, the present invention provides a hairpin RNA which formsthe double-stranded RNA in a cell, in which an RNA homologous with apart of an mRNA transcribed from a genomic RNA of influenza B viruses islinked to antisense RNA thereof by a linker sequence.

It is not necessary to anneal two kinds of single-stranded RNA to form adouble-stranded RNA in order to create the hairpin RNA because it can becreated from one kind of RNA through chemical synthesis and the like,and thus handling of the hairpin RNA is easy. Furthermore, because thehairpin RNA forms double-stranded RNA in a cell, it exerts an RNAinterference activity and can inhibit replication of influenza Bviruses.

The double-stranded RNA preferably inhibits all of the followinginfluenza B virus strains: B/Johannesburg/5/99 strain, B/Shangdong/07/97strain, B/Hong Kong/8/73 strain, B/Shanghai/361/2002 strain, andB/Victoria/2/87 strain.

Even if influenza virus strains undergo mutation, it is highly possiblethat double-stranded RNA which can inhibit replication of all of theinfluenza virus strains described above will be still effective.

The present invention provides an expression vector for adouble-stranded RNA which contains a first DNA complimentary to an RNAselected from the group consisting of RNA of nucleotide sequences as setforth in SEQ ID NOs: 1 to 57 or an RNA selected from the groupconsisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1to 57 in which 1 to 3 nucleotide(s) is/are substituted and a second DNAcomplimentary to the first DNA, as well as promoters on 5′ sides of eachof the first DNA and the second DNA, in which, in a cell to which thevector is introduced, the vector transcribes a first RNA complimentaryto the first DNA and a second RNA complimentary to the second DNA, andthe first RNA and the second RNA hybridize to each other to formdouble-stranded RNA.

Furthermore, the present invention provides an expression vector for adouble-stranded RNA which contains a first DNA complimentary to an RNAselected from the group consisting of RNA of nucleotide sequences as setforth in SEQ ID NOs: 1 to 57 or an RNA selected from the groupconsisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1to 57 in which 1 to 3 nucleotide(s) is/are substituted, in which the RNAhas an RNA having 1 to 4 nucleotide(s) attached to a 3′ end thereof, anda second DNA complimentary to an RNA which is an antisense RNA of an RNAselected from the group consisting of RNA of nucleotide sequences as setforth in SEQ ID NOs: 1 to 57 or antisense RNA of RNA selected from thegroup consisting of RNA of nucleotide sequences as set forth in SEQ IDNOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, in whichthe RNA has an RNA having 1 to 4 nucleotide(s) attached to a 3′ endthereof, as well as promoters on 5′ sides of each of the first DNA andthe second DNA, in which, in a cell to which the vector is introduced,the vector transcribes a first RNA complimentary to the first DNA and asecond RNA complimentary to the second DNA, and the first RNA and thesecond RNA hybridize to each other to form a double-stranded RNA.

Still further, the present invention provides an expression vector for ahairpin RNA which contains a DNA strands encoding a hairpin RNA, inwhich an antisense DNA complimentary to an RNA selected from the groupconsisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1to 57 or an antisense DNA complimentary to an RNA selected from thegroup consisting of RNA of nucleotide sequences as set forth in SEQ IDNOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted is linkedto a DNA complimentary to the antisense DNA by a linker sequence, aswell as promoters on 5′ sides of the DNA strands, in which, in a cell towhich the vector is introduced, the vector transcribes the hairpin RNA,and the hairpin RNA is processed inside the cell to form adouble-stranded RNA.

When the vector is introduced into a cell, a double-stranded RNA causingRNA interference is continuously transcribed within the cell, therebyreplication of influenza B viruses can be inhibited for a long term.

The vector is preferably a plasmid vector or a viral vector toefficiently express a double-stranded RNA in mammalian cells.

Also, the double-stranded RNA, the hairpin RNA, or the vector can beused as a pharmaceutical composition or an anti-influenza virus agentbecause it can inhibit replication of influenza B viruses whenintroduced into mammalian cells.

The pharmaceutical compositions or the anti-influenza virus agents cancontain a plurality of the double-stranded RNA, the hairpin RNA, or thevector. As shown in Examples, in some cases no effect is exerted oncertain kinds of virus strains depending on a sequence ofdouble-stranded RNA, however, there are cases in which an effect can beexerted on such strains by employing a plurality of double-stranded RNAconcurrently.

Also, as shown in Examples, in some cases an effect diminishes over timewhen one of double-stranded RNA is used, however, there are cases inwhich an effect sustains for a longer period of time by employing aplurality of double-stranded RNA concurrently.

Furthermore, the double-stranded RNA or the hairpin RNA, ordouble-stranded RNA produced from the vector has an activity tospecifically cleave an mRNA derived from influenza B viruses so that akit containing the double-stranded RNA, the hairpin RNA, or the vector,and a transfection reagent can be used as a detection kit for influenzaB viruses.

The pharmaceutical compositions or the anti-influenza virus agents canfurther contain a double-stranded RNA which inhibits replication ofinfluenza A viruses by RNA interference.

The above-described pharmaceutical compositions or the anti-influenzavirus agents can exert their therapeutic effects regardless of ifinfectious pathogens are influenza A viruses or influenza B viruses, andtherefore even if superinfection due to a simultaneous infection withboth strains occur, it can still be treated.

EFFECT OF THE INVENTION

An infectious disease caused by influenza B viruses can be effectivelytreated and prevented by introducing the double-stranded RNA, thehairpin RNA, and the vector of the present invention into mammaliancells. Furthermore, the double-stranded RNA of the present invention hasan activity to inhibit replication of plural kinds of influenza B virusstrains, therefore, in a case if influenza B viruses having mutation ina sequence targeted by the double-stranded RNA arise, mRNA derived fromthe viruses are still cleaved and replication of the influenza B virusescan be inhibited. For this, even when an epidemic strain of influenza Bviruses is unknown, a therapeutic effect can be exerted on an infectiousdisease caused by influenza B viruses.

The pharmaceutical compositions and the anti-influenza virus agents ofthe present invention can contain two or more kinds of double-strandedRNA at the same time. For example, at least one kind of double-strandedRNA designed to target influenza A viruses and at least one kind ofdouble-stranded RNA designed to target influenza B viruses can be usedconcurrently. This way of usage enables application of thepharmaceutical compositions of the present invention regardless of ifinfectious pathogens are influenza A viruses or influenza B viruses, andeven if superinfection due to a simultaneous infection with both strainsis caused, it can still be treated. For another example, at least two ormore kinds of double-stranded RNA designed to target influenza B virusescan be used concurrently. This way of usage can expand and enhance aneffect of double-stranded RNA in a case in which infectious pathogensare influenza B viruses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows steps of screening of double-stranded RNA which inhibitsreplication of influenza B viruses by a transfection microarray;

FIG. 2 (A) shows inhibition rates of double-stranded RNA NP-1496 alone,B-NP-1999-13 alone, as well as a combination of NP-1496 and B-NP-1999-13for influenza virus B/Johannesburg/5/99 strain, and (B) shows inhibitionrates of double-stranded RNA NP-1496 alone, B-NP-1999-13 alone, and acombination of NP-1496 and B-NP-1999-13 for influenza virus A/PR/8/34strain;

FIG. 3 (A) shows inhibition rates of double-stranded RNA B-PB2-1997-7alone, B-PB1-1999-1 alone, as well as a combination of B-PB2-1997-7 andB-PB1-1999-1 for influenza virus B/Shanghai/361/2002 strain, and (B)shows inhibition rates of double-stranded RNA B-PB2-1997-7 alone,B-PB1-1999-1 alone, as well as a combination of B-PB2-1997-7 andB-PB1-1999-1 for influenza virus B/Shangdong/07/97 strain; and

FIG. 4 (A) shows inhibition rates of double-stranded RNA B-NP-1999-3alone, B-NP-1999-13 alone, as well as a combination of B-NP-1999-3 andB-NP-1999-13 for influenza virus B/Shanghai/361/2002 strain in 18-hourculture, and (B) shows inhibition rates of double-stranded RNAB-NP-1999-3 alone, B-NP-1999-13 alone, as well as a combination ofB-NP-1999-3 and B-NP-1999-13 for influenza virus B/Shangdong/07/97strain in 18-hour culture, and (C) shows inhibition rates ofdouble-stranded RNA B-NP-1999-3 alone, B-NP-1999-13 alone, as well as acombination of B-NP-1999-3 and B-NP-1999-13 for influenza virusB/Shanghai/361/2002 strain in 30-hour culture, and (D) shows inhibitionrates of double-stranded RNA B-NP-1999-3 alone, B-NP-1999-13 alone, aswell as a combination of B-NP-1999-3 and B-NP-1999-13 for influenzavirus B/Shangdong/07/97 strain in 30-hour culture.

DESCRIPTION OF SYMBOLS

1 . . . spot position, 2 . . . spotter, 3 . . . glass slide, 4 . . .double-stranded RNA microarray, 5 . . . cell suspension, 6 . . . petridish, 7 . . . influenza B virus solution, 8 . . . staineddouble-stranded RNA microarray

BEST MODES FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention are describedhereinbelow.

A double-stranded RNA of the present invention is described.

The double-stranded RNA of the present invention is characterized bybeing double-stranded RNA which inhibits replication of influenza Bviruses by RNA interference, in which the double-stranded RNA comprisesan RNA having 19 to 25 nucleotide(s) homologous with a part of an mRNAtranscribed from a genomic RNA of influenza B viruses and antisense RNAthereof.

The phrase “inhibits replication of influenza B viruses by RNAinterference” does not mean directly inhibiting synthesis of proteinwhich constructs influenza viruses but it means inhibiting by cleavingan mRNA of a target viral gene sequence-specifically, and it includestransient inhibition of viral replication.

The above statement similarly applies to a case in which adouble-stranded RNA “inhibits replication of influenza A viruses by RNAinterference.”

“RNA” is one of the nucleic acids and it refers to a polymer ofribonucleotides consisting of ribose, phosphoric acid, and bases (i.e.,adenine, guanine, cytosine, or uracil). RNA can take structure ofsingle-stranded, double-stranded, or hairpin RNA because it can form acomplementary hydrogen bond similarly to DNA.

An RNA can be synthesized based on a conventional synthetic method. Forexample, it can be synthesized by a nucleic acid synthesizing machine orby transcribing a DNA template in vitro (i.e., in vitro transcription).At that time a mixed group of short double-stranded RNA having 19 to 25by can be obtained by subjecting long double-stranded RNA synthesized inadvance to dicer enzyme treatment.

The term “influenza B viruses” refers to RNA viruses which belong toorthomyxoviridae and infect humans to cause influenza. Influenza Bviruses have viral genes encoding hemagglutinin (HA), neuraminidase(NA), NB protein (NB), RNA polymerase PA subunit (PA), RNA polymerasePB1 subunit (PB1), RNA polymerase PB2 subunit (PB2), M1 protein (M1),BM2 protein (BM2), NP protein (nuclear protein; NP), and NS protein(nonstructural protein; NS) in RNA genome which is consisted ofnegative-strand, single-stranded RNA.

When influenza B viruses infect humans, mRNA of each viral gene istranscribed from a genomic RNA template by the viruses' ownRNA-dependent RNA polymerases, followed by synthesis of each viralprotein by ribosomes of a host cell. Then, a set of viral genome whichhas been replicated through a different pathway and the viral proteinthus produced assembles within the cell, thereby a virus particle isreplicated. As described above, the translation products of the viralgene are essential for replication of influenza B viruses, and aninfection caused by influenza B viruses can be treated or prevented, ifexpression of the gene is inhibited.

The double-stranded RNA is produced by synthesizing RNA having 19 to 25nucleotides which are homologous with a part of an mRNA of ahemagglutinin (HA) gene, a neuraminidase gene, a NB protein gene, an RNApolymerase PA subunit gene, an RNA polymerase PB1 subunit gene, an RNApolymerase PB2 subunit gene, a M1 protein gene, a BM2 protein gene, anNP protein gene, and a NS protein gene of influenza B viruses as well asan antisense RNA thereof each separately, and annealing the RNA thussynthesized.

In order to strongly inhibit replication of influenza B viruses, atarget mRNA is preferably an mRNA of an NP protein gene, an RNApolymerase PA subunit gene, an RNA polymerase PB1 subunit gene, or anRNA polymerase PB2 subunit gene of influenza B viruses, among which itis more preferably an mRNA of an NP protein gene.

Nucleotide sequences of each influenza B viral gene is open to thepublic by genetic database such as GenBank, and an RNA which constructsdouble-stranded RNA can be designed based on such available nucleotidesequence information.

The RNA is preferably selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or selectedfrom the group consisting of RNA of nucleotide sequences as set forth inSEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted,and it is more preferably selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 11 or selectedfrom the group consisting of RNA of nucleotide sequences as set forth inSEQ ID NOs: 1 to 11 in which 1 to 3 nucleotide(s) is/are substituted.

The nucleotide sequences shown in SEQ ID NOs: 1 to 57 are a partialsequence of an mRNA of an NP protein gene, an RNA polymerase PA subunitgene, an RNA polymerase PB1 subunit gene, and an RNA polymerase PB2subunit gene of influenza B viruses, and RNA which constructsdouble-stranded RNA can be designed based on the nucleotide sequenceinformation of the above genes.

The RNA can contain one or more modified ribonucleotide(s) to attainresistance to degradation by ribonucleases, and a ribonucleotide inwhich 2′-OH group of a ribose ring is substituted with a fluoro group, amethyl group, a methoxyethyl group, or a propyl group is exemplified asthe modified nucleotide.

A ribose ring which is to undergo substitution can be pyrimidine,purine, or a combination thereof. Among them, pyrimidine, for example,cytosine, a cytosine derivative, uracil, a uracil derivative, or acombination thereof is preferred. Either of a sense RNA strand and anantisense RNA strand, or both RNA strands of a double-stranded RNA cancontain the modified ribonucleases to protect an RNA from degradation byribonucleases.

One or more phosphodiester bond(s) of an RNA can be substituted withphosphorothioate bond(s) to make the RNA resistant to degradation byribonucleases.

A person skilled in the art can carry out substitution of a 2′-OH groupof a ribose ring with another functional group and a phosphodiester bondwith a phosphorothioate bond based on a conventional method of chemicalsynthesis.

An epidemic strain of influenza B viruses is broadly classified into twogroups, namely B/Victoria/2/87 and B/Yamagata/16/88, according todifferences in the antigenicity of hemagglutinin (HA), and a virusstrain which circulates every year is a different virus strain belongingto either group. Influenza B viruses include, for example,B/Johannesburg/5/99 strain, B/Shangdong/07/97 strain, B/Hong Kong/8/73strain, B/Shanghai/361/2002 strain, and B/Victoria/2/87 strain.

The double-stranded RNA preferably inhibits replication of two or moreof the virus strains of B/Johannesburg/5/99 strain, B/Shangdong/07/97strain, B/Hong Kong/8/73 strain, B/Shanghai/361/2002 strain, andB/Victoria/2/87 strain, all of which are influenza B viruses, morepreferably inhibits replication of three or more of the virus strains,and even more preferably inhibits replication of all of the virusstrains.

The double-stranded RNA has preferably 19 to 25 bp, more preferably 19to 23 bp, and even more preferably 19 to 21 by in order to avoidinduction of interferon and subsequent apoptosis in mammalian cells.

The double-stranded RNA of the present invention preferably formsoverhanging ends by having DNA or RNA having 1 to 4 nucleotide(s)attached to 3′ ends of the sense and the antisense strands thereof, andit is more preferable that the overhanging ends are DNA or RNAconsisting of 2 nucleotides. Also, the nucleotide sequence of theoverhanging end of the antisense strand of the double-stranded RNA ispreferably complimentary to an mRNA of a target gene, however, that isnot essential, and it is acceptable as long as DNA or RNA having anarbitrary nucleotide sequence is attached to a 3′ end thereof.Furthermore, the overhanging end preferably consists of DNA.

The hairpin RNA of the present invention is characterized in that it ishairpin RNA which forms the double-stranded RNA in a cell, in which anRNA homologous with a part of an mRNA transcribed from a genomic RNA ofinfluenza B viruses is linked to antisense RNA thereof by a linkersequence. An arbitrary sequence can be used for a linker sequence aslong as it does not block formation of a hairpin structure, while thelinker sequence is preferably 4 to 6 nucleotides-long, more preferably 4nucleotides-long.

Screening of double-stranded RNA which inhibits replication of influenzaB viruses can be carried out by, for example, introducingdouble-stranded RNA into an animal cell such as an MDCK cell andsubsequently infecting the cell by influenza B viruses, and observing tosee if apoptosis is induced in the cell as an indication.

That is to say, if double-stranded RNA which cleaves an mRNA derivedfrom influenza B viruses is introduced into a cell, replication of theviruses is inhibited and apoptosis will not be induced in an animalcell, even if the cell is invaded by influenza B viruses. Therefore, ifthe cell survives, the double-stranded RNA introduced into the cell canbe judged as double-stranded RNA which inhibits replication of influenzaB viruses. On the other hand, if double-stranded RNA which does notcleave mRNA derived from influenza B viruses is introduced into a cell,viruses are replicated and eventually apoptosis will be induced in thecell. Furthermore, because cells in which apoptosis is induced will dieout and detach from a culture plate, an activity of double-stranded RNAwhich inhibits replication of influenza B viruses, which is hereinafterdescribed as an anti-influenza virus activity, can be determined basedon a ratio of viable cells adhering to the culture plate.

The screening can be carried out using a transfection microarray. Asolid phase gene transfer technology of CytoPathfinder, Inc. can beemployed for a system of transfection microarray, for example.

A screening using a transfection microarray starts with spottingrandomly-synthesized double-stranded RNA onto a glass slide to produce adouble-stranded RNA microarray. At that time a correlation between anucleotide sequence of double-stranded RNA and a respective spotposition is compiled in a database to know which double-stranded RNA isspotted on which spot position on the glass slide.

Subsequently, the double-stranded RNA microarray is placed in a petridish and fixed thereto, to which a suspension containing MDCK cells andculture media is poured to seed the cells on the double-stranded RNAmicroarray. After one day of culture, the double-stranded RNA spotted onthe double-stranded RNA microarray is introduced into the cells throughthe cell membrane. Therefore, if the cells are cultured with addition ofsolution containing influenza B viruses into the medium, cells whichhave survived without induction of apoptosis will keep adhering tospecific spot positions on the double-stranded RNA microarray, whilecells in which apoptosis has been induced will detach from thedouble-stranded RNA microarray. The double-stranded RNA having ananti-influenza virus activity can then be screened based on spotpositions to which the cells are adhering as an indicator. Namely, thenucleotide sequence of double-stranded RNA having an anti-influenzavirus activity can be obtained based on information of the spot positionto which the cells are adhered.

The vector of the present invention is then described.

A first aspect of the vector of the present invention is characterizedin that it is an expression vector for a double-stranded RNA whichcontains a first DNA complimentary to an RNA selected from the groupconsisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1to 57 or an RNA selected from the group consisting of RNA of nucleotidesequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3nucleotide(s) is/are substituted and a second DNA complimentary to thefirst DNA, as well as promoters on 5′ sides of each of the first DNA andthe second DNA, in which, in a cell to which the vector is introduced,the vector transcribes a first RNA complimentary to the first DNA and asecond RNA complimentary to the second DNA, and the first RNA and thesecond RNA hybridize to each other to form double-stranded RNA.

For example, a vector in which a DNA which encodes a sense strand ofdouble-stranded RNA is linked to a first promoter in a controllable wayand a DNA which encodes an antisense strand of double-stranded RNA islinked to a second promoter in a controllable way can be exemplified. Inthat case, the sense and the antisense strands of the double-strandedRNA are transcribed each independently, and the promoters for eachstrand can be identical or different from each other.

The above aspect can be an expression vector for double-stranded RNAwhich contains a first DNA complimentary to an RNA selected from thegroup consisting of RNA of nucleotide sequences as set forth in SEQ IDNOs: 1 to 57 or an RNA selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3nucleotide(s) is/are substituted, in which the RNA has an RNA having 1to 4 nucleotide(s) attached to 3′ ends thereof, and a second DNAcomplimentary to an RNA which is an antisense RNA of an RNA selectedfrom the group consisting of RNA of nucleotide sequences as set forth inSEQ ID NOs: 1 to 57 or an antisense RNA of an RNA selected from thegroup consisting of RNA of nucleotide sequences as set forth in SEQ IDNOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, in whichthe RNA has an RNA having 1 to 4 nucleotide(s) attached to 3′ endsthereof, as well as promoters on 5′ sides of each of the first DNA andthe second DNA, and the vector transcribes a first RNA complimentary tothe first DNA and a second RNA complimentary to the second DNA, in whichthe first RNA and the second RNA subsequently hybridize to each other toform double-stranded RNA in a cell to which the vector is introduced.

A second aspect of the vector of the present invention is characterizedin that it is an expression vector for a hairpin RNA which contains DNAstrands encoding a hairpin RNA, in which an antisense DNA complimentaryto an RNA selected from the group consisting of RNA of nucleotidesequences as set forth in SEQ ID NOs: 1 to 57 or an antisense DNAcomplimentary to RNA selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3nucleotide(s) is/are substituted is linked to a DNA complimentary to theantisense DNA by a linker sequence, as well as promoters on 5′ sides ofthe DNA strands, in which, in a cell to which the vector is introduced,the vector transcribes the hairpin RNA, and the hairpin RNA is processedinside the cell to form double-stranded RNA.

For example, a vector containing a DNA encoding a hairpin RNA, in whichthe DNA encoding sense and antisense strands of double-stranded RNA arelinked by a linker sequence, is controllably linked to a uniformpromoter can be exemplified. In that case, a single-stranded RNA, inwhich a sense strand and an antisense strand of double-stranded RNA arelinked by a linker sequence, is produced. The sense strand part and theantisense strand part of the single-stranded RNA anneal to form hairpinRNA. An arbitrary sequence can be used for a linker sequence as long asthe sequence does not block formation of a hairpin structure, while thelinker sequence is preferably 4 to 6 nucleotides-long, more preferably 4nucleotides-long.

The vector is used to create a double-stranded RNA which inhibitsreplication of influenza B viruses by genetic recombination technology,and it can be a vector which can transcribe a target RNA to createdouble-stranded RNA in a host cell. The vector can be in a form ofplasmid or virus and contain an origin of replication, a terminator, aselection marker such as a neomycin resistant gene, a tetracyclineresistant gene, and an ampicillin resistant gene besides a promoter, andcan further contain an enhancer, a polyadenylation signal, and the likeas needed.

A plasmid vector can be, for example, pcDNA3, pUC, pBR322, andpBluescript, and a viral vector can be an adenovirus, a retrovirus, alentivirus, a baculovirus, a vaccinia virus, and the like.

A DNA to be incorporated into a vector as a template for an RNA can besynthesized by a method known in the art, and it can be inserted undercontrol of an appropriate promoter which directs RNA transcriptionalsynthesis.

A promoter can be exemplified as a CMV promoter, a HSV thymidine kinasepromoter, a SV40 promoter, a retroviral LTR, and a metallothioneinpromoter, and further, a U6 promoter or a H1 promoter, both of which areRNA polymerase III promoters. Also, the promoter can be an induciblepromoter which enables alternation between “on” and “off” of expression.

A molecular biological technique necessary for construction of a vectoris described in Molecular Cloning A Laboratory Manual (Sambrook, et al.,Cold Spring Harbor, N.Y., 1989).

Further, the double-stranded RNA, the hairpin RNA, or the vector can beused as a pharmaceutical composition or an anti-influenza virus agentwhich aims to treat and prevent an infection caused by influenza Bviruses.

The pharmaceutical compositions and the anti-influenza virus agentscontain at least one kind of the double-stranded RNA, the hairpin RNA,or the vector as an active ingredient, and can further containpharmaceutically acceptable additives as needed.

Also, because double-stranded RNA, the hairpin RNA, or double-strandedRNA produced from the vector can specifically cleave mRNA of a targetgene of influenza B viruses, they can be used as a detection kit forinfluenza B viruses which exploits their such characteristic properties.

The detection kit is characterized by containing a transfection reagentin addition to the double-stranded RNA, the hairpin RNA, or the vector.

The transfection reagent can be, for example, a reagent containinglipid, in which the lipid and an objective vector form a complex,thereby the vector is introduced into a target cell. Lipid suitable fora transfection reagent can be exemplified as, for example, polyaminelipid, cationic lipid, polycationic lipid, cholesterol, neutral lipid,and cationic polyamine lipid.

The pharmaceutical composition and the anti-influenza virus agent canfurther contain a double-stranded RNA which inhibits replication ofinfluenza A viruses by RNA interference. A Double-stranded RNA whichinhibits replication of influenza A viruses is publicly known, and forexample, ones described in the specifications of US2006/0160759 andUS2006/0275265, and WO2004/028471 and WO2006/102461 can be preferablyused.

EXAMPLES

The present invention is described more specifically with exampleshereinbelow, however, the present invention is not limited to theseexamples in any way.

(Design and Synthesis of Double-Stranded RNA)

Based on nucleotide sequence information of 8 kinds of viral genes ofinfluenza B virus B/Johannesburg/5/99 strain, which was obtained asGenBank accession nos. of CY018613 (hemagglutinin gene), CY018614 (M1protein gene and BM2 protein gene), CY018615 (neuraminidase gene and NBprotein gene), CY018616 (NP protein gene), CY018617 (NS1 protein geneand NS2 protein gene), CY018618 (RNA polymerase PA subunit gene),CY018619 (RNA polymerase PB1 subunit gene), CY018620 (RNA polymerase PB2subunit gene), 2360 kinds of double-stranded RNA having 19 to 25nucleotides complementary to a partial sequence of the above genes andantisense RNA thereof were designed to obtain double-stranded RNA whichcould cleave mRNA transcribed from the viral genes of influenza Bviruses by RNA interference. Sequences of an mRNA targeted by thedouble-stranded RNA for RNA interference are as set forth in SEQ ID NOs:1 to 2360.

When designing double-stranded RNA, sequences which could induce RNAinterference were selected in reference to literature by Khvorova A. etal. (Cell, 2003, Vol. 115, No. 2, p. 209-216), literature by Schwarz DS. et al. (Cell, 2003, Vol. 115, No. 2, p. 199-208), literature by HsiehA C. et al. (Nucl. Acids Res., 2004, Vol. 32, No. 3, p. 893-901),literature by Reynolds A. et al. (Nat. Biotechnol., 2004, Vol. 22, No.3, p. 326-330) and literature by Ui-Tei K. et al. (Nucl. Acids Res.,2004, Vol. 32, No. 3, p. 936-948).

From 2360 kinds of double-stranded RNA thus designed, 80 kinds ofdouble-stranded RNA were selected. From the selected RNA, an RNA havingsequences homologous with an mRNA transcribed from viral genes ofinfluenza B viruses, in which 2 dTTP were attached to a 3′ end thereof,and an RNA which was an antisense RNA thereof, in which 2 nucleotides ofDNA complementary to the mRNA were attached to a 3′ end thereof based onthe nucleotide sequence information, were each chemically synthesized. Aset of an equal number of moles of the RNA and the antisense RNA thereofthus synthesized was mixed in annealing buffer (i.e., 100 mM KOAc, 2 mMMgOAc, 30 mM HEPES-KOH, pH 7.4), followed by denaturation treatment for5 minutes at 90° C. Subsequently, annealing was carried out byincubation for one hour at 37° C., thereby double-stranded RNA wasobtained.

(Method for Screening of Double-Stranded RNA by a TransfectionMicroarray)

FIG. 1 shows steps of screening of double-stranded RNA which inhibitsreplication of influenza B viruses by a transfection microarray.

A mixed solution of double-stranded RNA was prepared following stepsshown in FIG. 1(A). Specifically, 25 μL of serum-free DMEM medium (i.e.,Dulbecco's Modified Eagle's Medium) was put in a microtube, to which 1to 10 μL of 100 μM double-stranded

RNA was added and mixed. Subsequently, 1 to 5 μL of a transfectionreagent (Lipofectamine 2000; Invitrogen Corporation) was added andmixed, and the resultant mixture was left to stand for 20 minutes.Thereafter, 10 to 200 μg of a cell-adhesion factor (fibronectin) wasadded to the solution in the microtube and mixed, thereby a mixedsolution of double-stranded RNA used to make a double-stranded RNAmicroarray 4 was prepared.

As shown in FIG. 1(B), a spotter 2 was then filled with the mixedsolution of double-stranded RNA and the solution was spotted onpredetermined spot positions 1 laid out on a glass slide 3, thereby thedouble-stranded RNA microarray 4 was prepared. At that time, as anegative control, a mixed solution of the double-stranded RNA which doesnot inhibit replication of influenza B viruses (QIAGEN Cat. No. 1022076;it will be hereinafter described as control double-stranded RNA) wasalso spotted on the same glass slide 3.

As to the double-stranded RNA microarray 4 thus prepared, a correlationbetween the spot positions 1 and the respective sequence information ofdouble-stranded RNA was compiled in a database to keep track ex-postfacto of which double-stranded RNA having a certain nucleotide sequencewas spotted on which spot position.

Thereafter, as shown in FIG. 1(B), the double-stranded RNA microarray 4was set in a petri dish 6, to which a cell suspension 5 containing MDCKcells was poured to seed the cells. The cells were let to adhere to thedouble-stranded RNA microarray 4 and cultured for one day at 37° C. As aresult, each double-stranded RNA spotted on the double-stranded RNAmicroarray 4 was to pass through the cell membrane of MDCK cells adheredto each spot position 1 to be introduced inside the cell.

Thereafter, 5 mL of influenza B virus solution 7 prepared to have atiter of 1.8×10⁷ pfu/mL was poured into the petri dish 6 and it wascultured for 23 to 47 hours at 37° C. As a result, viral replication wasto occur within the MDCK cells, and cells in which apoptosis was inducedwas to detach from the double-stranded RNA microarray 4.

Thereafter, the double-stranded RNA microarray 4 was taken out from thepetri dish 6 and washed with PBS, and surviving viable cells on thedouble-stranded RNA microarray 4 were fixed with ethanol. The fixedviable cells were then stained with crystal violet. A staineddouble-stranded RNA microarray 8 was air dried and scanned by a DNAmicroarray scanner (GenePix4200) to obtain a fluorescent image used foranalysis of the spot positions 1 containing surviving viable cells.

The fluorescent image thus obtained was analyzed by an image analysissoftware (GenePix Pro Ver.6.0) to computate a total number of pixels ineach of the spot positions 1. An anti-influenza virus activity andstrength thereof can be evaluated based the total number of pixelsbecause it is a value corresponding to an area of surviving cells and anumber of viable cells.

Screening of double-stranded RNA by a transfection microarray wasrepeatedly carried out using 6 sheets of the double-stranded RNAmicroarray 4 in which the spot position 1 of each double-stranded RNAwas differed. Then, a statistical hypothesis testing was conducted asdescribed below between the total number of pixels in the spot position1 of each double-stranded RNA and the total number of pixels in the spotposition 1 of the control double-stranded RNA. Double-stranded RNA forwhich a statistical difference was confirmed in 4 or more out of 6sheets was judged to be double-stranded RNA having an anti-influenzavirus activity.

Steps of Statistical Hypothesis Testing:

1. Normalities of the total number of pixels in the spot position of thecontrol double-stranded RNA and the total number of pixels in the spotposition of each double-stranded RNA obtained through 6 sheets of thedouble-stranded RNA microarray were checked (W-test, level ofsignificance of 10%). When the values of both groups were found to be inaccordance with the normal distribution, differences in mean valuesbetween 2 groups were tested (proceeding to step 2). Meanwhile, when thetotal number of pixels of either one of the groups was not in accordancewith the normal distribution, differences in measures of centraltendency between 2 groups were nonparametrically tested (proceeding tostep 5).

2. Homoscedasticities of the total number of pixels in the spot positionof the control double-stranded RNA and the total number of pixels in thespot position of each double-stranded RNA were tested (F-test, level ofsignificance of 25%, two-sided test). When they were homoscedastic, aStudent's t-test was conducted (step 3), and when they werenon-homoscedastic, a Welch's t-test was conducted (step 4).

3. Differences in mean values between the total number of pixels in thespot position of the control double-stranded RNA and the total number ofpixels in the spot position of each double-stranded RNA were tested by aStudent's t-test (level of significance of 1%, one-sided test).

4. Differences in mean values between the total number of pixels in thespot position of the control double-stranded RNA and the total number ofpixels in the spot position of each double-stranded RNA were tested by aWelch's t-test (level of significance of 1%, one-sided test).

5. Differences in measures of central tendency between the total numberof pixels in the spot position of the control double-stranded RNA andthe total number of pixels in the spot position of each double-strandedRNA were tested by a Mann-Whitney's U-test (level of significance of 1%,one-sided test).

Furthermore, among the double-stranded RNA judged to have ananti-influenza virus activity, double-stranded RNA having an average S/Nratio (Signal to Noise ratio) of 3 or greater was judged to be adouble-stranded RNA having a remarkable anti-influenza virus activity.

A S/N ratio described here refers to a ratio between a signal intensityobtained from a negative control (N) and a signal intensity obtainedfrom a sample to be evaluated (S) in a screening system using amicroarray, and it is used as an indication to represent strength of RNAinterference effect in a screening of double-stranded RNA by atransfection microarray. Specifically, a S/N ratio is a value defined bythe following formula using a mean value of the total number of pixelsin the spot position of each double-stranded RNA which has been verifiedto have an anti-influenza virus activity by the statistical hypothesistesting (i.e., μ_(sample)), a mean value of the total number of pixelsin the spot position of the control double-stranded RNA (i.e., μ_(neg)),and unbiased standard deviation (i.e., δ_(neg)).

S/N ratio=μ_(sample)−μ_(neg)/δ_(neg)

The number of surviving cells in each spot position represents strengthof RNA interference effect in the present screening method, therefore,how much the total number of pixels in the spot position of eachdouble-stranded RNA which has been confirmed to have a significantdifference by the statistical hypothesis testing exceeds the totalnumber of pixels in the spot position of the control double-stranded RNAcan be evaluated by a S/N ratio.

When a distribution of the total number of pixels in the spot positionof the control double-stranded RNA conforms with the normaldistribution, the unbiased standard deviation (δ_(neg)) corresponds to aflexion point of a normal distribution curve and 99.73% of data will beincluded within a range of μ_(neg)±3δ_(neg). In that case, when adetection limit of the S/N ratio is set as 3 or greater, the differencesbetween the mean values will be 3δ_(neg) or greater according to theabove formula. Therefore, it is assured that the mean value of the totalnumber of pixels in the spot positions of the double-stranded RNA willnot be included within the range of 99.73% of the distribution of thetotal number of pixels in the spot position of the controldouble-stranded RNA.

A S/N ratio was calculated after normalizing (or standardizing) thetotal number of pixels in the spot positions of the double-stranded RNAfollowing the below-described steps considering that 6 sheets of thedouble-stranded RNA microarray were employed for investigation of theanti-influenza virus activity in the present screening method.

1. For each double-stranded RNA microarray, the total number of pixelsin the spot position of each double-stranded RNA was normalized usingthe mean value of the total number of pixels in the spot position of thecontrol double-stranded RNA (i.e., μ_(neg)) and the unbiased standarddeviation (i.e., δ_(neg)).

2. A S/N ratio was calculated using the normalized total number ofpixels in the spot position of each double-stranded RNA.

3. Double-stranded RNA of mean S/N ratio of 3 or greater was judged asdouble-stranded RNA having a remarkable anti-influenza virus activity.

In the above screening method, if double-stranded RNA which cleaves mRNAderived from influenza B viruses is introduced into MDCK cells,replication of the viruses is inhibited within the cells in a case whenthe MDCK cells is invaded by influenza B viruses, and consequentlyapoptosis will not be induced. Therefore, if the cells are viable andkeep adhering to the spot positions 1, the double-stranded RNAintroduced into the cells are judged as double-stranded RNA whichinhibits replication of influenza B viruses, and it will be judged thatthe greater the total number of pixels in the spot position 1, thestronger the activity of inhibiting replication of influenza B viruses.On the other hand, if double-stranded RNA which does not cleave mRNAderived from influenza B viruses is introduced into MDCK cells,replication of the viruses proceeds within the cells and eventuallyapoptosis will be induced. Because cells in which apoptosis has beeninduced detach from the double-stranded RNA microarray 4, when cellsdetach from a spot position 1, double-stranded RNA introduced into thecells will be judged as double-stranded RNA which is not capable ofinhibiting replication of influenza B viruses.

Accordingly, as long as spot positions 1 to which surviving cells areadhered are known, nucleotide sequences of double-stranded RNA having ananti-influenza virus activity is revealed by searching through thedatabase constructed in advance.

For screening using the transfection microarray, Transfection MicroArray(trademark) of CytoPathfinder, Inc. was employed.

EXAMPLE 1 Screening of Double-Stranded RNA which Inhibits Replication ofInfluenza B Virus B/Johannesburg/5/99 Strain

Double-stranded RNA which inhibits replication of influenza B virusB/Johannesburg/5/99 strain was screened out from 80 kinds of synthesizeddouble-stranded RNA according to the screening method of double-strandedRNA by the transfection microarray. At that time culture time afteraddition of the virus strain was set as 34 hours.

Table 1 shows nucleotide sequences of antisense and sense strands ofdouble-stranded RNA which inhibited viral replication caused by aninfection with influenza B virus B/Johannesburg/5/99 strain and blockedinduction of apoptosis. Double-stranded RNA which has a circle in thecolumn titled “S/N ratio≧3” means double-stranded RNA which has anaverage S/N ratio of 3 or greater and a remarkable anti-influenza virusactivity against viral replication.

TABLE 1 Double-stranded Nucleotide sequence  SEQ Nucleotide sequence SEQ RNA ID of an antisense strand ID No of a sense strand ID No S/N ≧ 3B-NP-1999-2 UUUGUUGCUUUAAUAAUCGag 2361 CGAUUAUUAAAGCAACAAAtt 2362 ○B-NP-1999-3 UUCAUUGACAGCAUUCUUCtt 2363 GAAGAAUGCUGUCAAUGAAtt 2364 ○B-NP-1999-4 UUAAUUGGAAUUUCAACGGga 2365 CCGUUGAAAUUCCAAUUAAtt 2366 ○B-NP-1999-5 UUAUUUGGCCAGACCCUCCgt 2367 GGAGGGUCUGGCCAAAUAAtt 2368 ○B-NP-1999-6 UUUAUCAUCUCUUACCAUCtt 2369 GAUGGUAAGAGAUGAUAAAtt 2370 ○B-NP-1999-8 UUGAUGUCUCUCAAUAGCCct 2371 GGCUAUUGAGAGACAUCAAtt 2372 ○B-NP-1999-10 UUAUCAUCUCUUACCAUCUtg 2373 AGAUGGUAAGAGAUGAUAAtt 2374 ○B-NP-1999-11 UAAAGUUCCACCUCCUUUGat 2375 CAAAGGAGGUGGAACUUUAtt 2376 ○B-NP-1999-12 UUGCUCUUCCUAUAAAUCGaa 2377 CGAUUUAUAGGAAGAGCAAtt 2378 ○B-NP-1999-13 UAGGCUUGAAUUCUGUGCCtg 2379 GGCACAGAAUUCAAGCCUAtt 2380 ○B-NP-1999-14 UUGGAUUAGGUUUCUCUCCat 2381 GGAGAGAAACCUAAUCCAAtt 2382 ○B-NP-1999-1 UUUAAUAAGAAUAAACACCca 2383 GGUGUUUAUUCUUAUUAAAtt 2384 ○B-NP-1999-7 UUAAUAAGAAUAAACACCCac 2385 GGGUGUUUAUUCUUAUUAAtt 2386 ○B-NP-1999-9 UUUAAUGGUGAUCUAGGCUtg 2387 AGCCUAGAUCAGCAUUAAAtt 2388 ○B-NP-1999-15 UUACGGAUUCGUUUGUUGCtt 2389 GCAACAAACGAAUCCGUAAtt 2390 ○B-PA-1999-1 UUUCAGACUUAAUUCAGCCtg 2391 GGCUGAAUUAAGUCUGAAAtt 2392B-PA-1999-2 UUCAUUUGGAUCUUAUUUGtg 2393 CAAAUAAGAUCCAAAUGAAtt 2394B-PA-1999-3 UAAUACAUUCUUCUAUUCCag 2395 GGAAUAGAAGAAUGUAUUAtt 2396B-PA-1999-4 UUAUUUGUGCCAUUCACUCgg 2397 GAGUGAAUGGCACAAAUAAtt 2398 ○B-PA-1999-6 UAUUGGGUCAGUUUGAUCCcg 2399 GGAUCAAACUGACCCAAUAtt 2400B-PA-1999-7 UUCAUUAACAAAGUAUUUCct 2401 GAAAUACUUUGUUAAUGAAtt 2402B-PA-1999-8 UUCCAUGCUAUUUCCCAGCtt 2403 GCUGGGAAAUAGCAUGGAAtt 2404B-PA-1999-9 UUCAUUUACUACUCUAUUGgt 2405 CAAUAGAGUAGUAAAUGAAtt 2406 ○B-PA-1999-10 UUAACAAAGUAUUUCCUUCtt 2407 GAAGGAAAUACUUUGUUAAtt 2408B-PA-1999-11 UUGUUCAACAAUUGCUUCCat 2409 GGAAGCAAUUGUUGAACAAtt 2410B-PA-1999-15 UUCCAGAAUACAUUCCCUCta 2411 GAGGGAAUGUAUUCUGGAAtt 2412 ○B-PA-1999-16 UCAUUUACUACUCUAUUGGtt 2413 CCAAUAGAGUAGUAAAUGAtt 2414B-PB1-1999-1 UUUAGUAUAGAUCUGUUCCtt 2415 GGAACAGAUCUAUACUAAAtt 2416 ○B-PB1-1999-3 UUAUUGGAGAACAAGACCGgt 2417 CGGUCUUGUUCUCCAAUAAtt 2418B-PB1-1999-5 UUUAUGAGGAAACCCUUUCtg 2419 GAAAGGGUUUCCUCAUAAAtt 2420B-PB1-1999-6 UUUAUAUUCAUCUUAAAGGct 2421 CCUUUAAGAUGAAUAUAAAtt 2422B-PB1-1999-7 UAGCAUAUUAAACAUUCCCat 2423 GGGAAUGUUUAAUAUCCUAtt 2424B-PB1-1999-8 UUUAUUGGAGAACAAGACCgg 2425 GGUCUUGUUCUCCAAUAAAtt 2426 ○B-PB1-1999-9 UUGUAAAUUCAAACAUUCCag 2427 GGAAUGUUUGAAUUUACAAtt 2428 ○B-PB1-1999-10 UAAUGAAUCAAUGAUAUCUtg 2429 AGAUAUCAUUGAUUCAUUAtt 2430B-PB1-1999-11 UUAGAUACAAAUCCAUCUCta 2431 GAGAUGGAUUUGUAUCUAAtt 2432 ○B-PB1-1999-13 UUCUUUAUAUUCUUUACUGag 2433 CAGUAAAGAAUAUAAAGAAtt 2434B-PB1-1999-15 UAUUCCACUCUGGAUAUCCtg 2435 GGAUAUCCAGAGUGGAAUAtt 2436 ○B-PB1-1999-18 UAUUCUUUCAGUCAUAGCCaa 2437 GGCUAUGACUGAAAGAAUAtt 2438B-PB1-1999-19 UAUCUUUCUAAUGGUAUGCta 2439 GCAUACCAUUAGAAAGAUAtt 2440B-PB1-1999-22 UUAGAUUGUACUUCAAUACta 2441 GUAUUGAAGUACAAUCUAAtt 2442B-PB1-1999-23 UUGUUCUUUAUUAUUGUCAtt 2443 UGACAAUAAUAAAGAACAAtt 2444B-PB1-1999-27 UUUAUUCCCAAUAAUUUACat 2445 GUAAAUUAUUGGGAAUAAAtt 2446B-PB1-1999-28 UUGUUCCUCAAGAAUCAUGtt 2447 CAUGAUUCUUGAGGAACAAtt 2448B-PB2-1999-5 UUUCUUACUCUUUCAACUGgg 2449 CAGUUGAAAGAGUAAGAAAtt 2450B-PB2-1999-7 UAUUCCACCAGGUAACUGCtg 2451 GCAGUUACCUGGUGGAAUAtt 2452 ○B-PB2-1999-10 UUUAAGUUGUAUUCCCUUGta 2453 CAAGGGAAUACAACUUAAAtt 2454B-PB2-1999-11 UUUGAUGCGACUAUUGAUCtt 2455 GAUCAAUAGUCGCAUCAAAtt 2456 ○B-PB2-1999-12 UUCAGUAUCUAUCACAGUCtt 2457 GACUGUGAUAGAUACUGAAtt 2458 ○B-PB2-1999-15 UUUAACUACUUUAACGGGCtt 2459 GCCCGUUAAAGUAGUUAAAtt 2460B-PB2-1999-16 UUUCUUAUUAUGUUAUAUUga 2461 AAUAUAACAUAAUAAGAAAtt 2462B-PB2-1999-18 UUGUAUUCCCUUGUAUUCCaa 2463 GGAAUACAAGGGAAUACAAtt 2464

As a result, a statistical difference was confirmed between 52double-stranded RNA and the control double-stranded RNA, of which 26double-stranded RNA had an average S/N ratio of 3 or greater.

EXAMPLE 2 Screening of Double-Stranded RNA which Inhibits Replication ofInfluenza B Virus Strains Other than B/Johannesburg/5/99 Strain

Among the 80 kinds of synthesized double-stranded RNA, 28double-stranded RNA which did not exhibit an anti-influenza activity forB/Johannesburg/5/99 strain were studied to find out if any of them hadan anti-influenza activity for other influenza B virus strains.

As influenza B viruses, B/Shangdong/07/97, B/Hong Kong/8/73,B/Shanghai/361/2002, and B/Victoria/2/87 strains were employed, and atest was carried out according to the method for screening ofdouble-stranded RNA by the transfection microarray in a similar mannerto Example 1.

However, because culture time needed for cell detachment to occur afteraddition of virus strains to a petri dish differed depending on thevirus strain, the culture time after addition of virus strains was setas follows: 23 hours for B/Shangdon/07/97 strain, 36 hours for B/HongKong/8/73 strain, 26 hours for B/Shanghai/361/2002 strain, and 47 hoursfor B/Victoria/2/87 strain.

Table 2 shows nucleotide sequences of antisense and sense strands ofdouble-stranded RNA which inhibited viral replication caused by aninfection with influenza B virus B/Shangdong/07/97, B/Hong Kong/8/73,B/Shanghai/361/2002, or B/Victoria/2/87 strains and blocked induction ofapoptosis. Double-stranded RNA which has a circle in the column titled“S/N ratio≧3” means double-stranded RNA which has an average S/N ratioof 3 or greater for one of the above virus strains and a remarkableanti-influenza virus activity against viral replication.

TABLE 2 Double-stranded Nucleotide sequence of SEQNucleotide sequence of SEQ RNA ID an antisense strand ID Noa sense strand ID No S/NL ≧ 3 B-PB2-1999-2 UAAAUCUUUCAUGUCUUCCtt 2465GGAAGACAUGAAAGAUUUAtt 2466 ○ B-PB2-1999-6 UUCAUUAAUUCAUUUAUCCca 2467GGAUAAAUGAAUUAAUGAAtt 2468 B-PB1-1999-17 UAAGGAUUUAUAUUCAUCUta 2469AGAUGAAUAUAAAUCCUUAtt 2470 B-PB1-1999-24 UUUCAUUUCAAUCAUUUGUtt 2471ACAAAUGAUUGAAAUGAAAtt 2472 B-PB1-1999-26 UUCAUCUUAAAGGCUCCGCtt 2473GCGGAGCCUUUAAGAUGAAtt 2474

As a result, a statistical difference was confirmed between 3double-stranded RNA (B-PB2-1999-02, B-PB1-1999-17, and B-PB1-1999-26)and the control double-stranded RNA against an infection caused byB/Shangdong/07/97 strain, of which 1 double-stranded RNA (B-PB2-1999-2)had an average S/N ratio of 3 or greater. A statistical difference wasconfirmed between 2 double-stranded RNA (B-PB2-1999-2 and B-PB1-1999-24)and the control double-stranded RNA against an infection caused byB/Hong Kong/8/73 strain, however, neither of them had a mean S/N ratioof 3 or greater. A statistical difference was confirmed between 1double-stranded RNA (B-PB2-1999-6) and the control double-stranded RNAagainst an infection caused by B/Shanghai/361/2002 strain, however, itdid not have a mean S/N ratio of 3 or greater. Meanwhile, a statisticaldifference was not observed between any double-stranded RNA and thecontrol double-stranded RNA against infection caused by B/Victoria/2/87strain.

Combined with the results obtained from Example 1, 57 double-strandedRNA exhibited an anti-influenza virus activity for one of the 5 strainsof influenza B viruses. Furthermore, 39 out of the 57 double-strandedRNA had a remarkable anti-influenza virus activity with a mean S/N ratioof 3 or greater for one of the virus strains. Accordingly, it waspresumed that one of the 57 double-stranded RNA could inhibit viralreplication and exert efficacy in treatment of influenza B viruses, evenif an influenza B virus strain which is to circulate from now forwardundergoes various mutations.

EXAMPLE 3 Screening of Double-Stranded RNA which Inhibits Replication ofa Plurality of Influenza B Virus Strains Simultaneously

Prediction of an influenza B virus strain to circulate is difficult, andeven if prediction comes true, the virus is highly prone to mutation,therefore, it is presumed that if one kind of double-stranded RNA caninhibit replication of a plurality of influenza B virus strains,treatment and prevention of an infection caused by influenza B virusesare realizable. In view of the above, among the 52 double-stranded RNAwhich exhibited an anti-influenza virus activity for influenza B virusB/Johannesburg/5/99 strain in Example 1, double-stranded RNA furtherhaving an anti-influenza virus activity for all virus strains ofB/Shangdong/07/97, B/Hong Kong/8/73, B/Shanghai/361/2002, andB/Victoria/2/87 strains was screened.

Screening was carried out according to the above-described method forscreening of double-stranded RNA by the transfection microarray in asimilar manner to Examples 1 and 2. In this screening, a double-strandedRNA microarray was used in which double-stranded RNA which has beenreported to inhibit replication of influenza B viruses (PB1-POS andPB2-POS) was spotted to a slide as a positive control in addition to the52 double-stranded RNA which exhibited an anti-influenza activity inExample 1. Both of PB1-POS and PB2-POS are double-stranded RNAcomprising nucleotide sequences identical to PB1-2196 and PB2-1999described in Antiviral Therapy (2006, Vol. 11, p. 431-438), and each ofthem was reported to cleave mRNA of an RNA polymerase PB1 subunit (PB1)gene and an RNA polymerase PB2 subunit (PB2) gene by RNA interference.

Table 3 shows double-stranded RNA IDs which inhibited viral replicationcaused by an infection with influenza B virus B/Johannesburg/5/99strain, B/Shangdong/07/97 strain, B/Hong Kong/8/73 strain,B/Shanghai/361/2002 strain, and B/Victoria/2/87 strain and blockedinduction of apoptosis as well as values of S/N ratio thereof.

TABLE 3 Values of S/N ratio Double-stranded B/Jonannesburg/ B/Shangdong/B/HongKong/ B/Shanghai/ B/Victoria/ RNA ID 5/99 strain 07/97 strain 8/73strain 361/2002 strain 2/87 strain PB1_POS 1.2 10.8 ND 3.0 ND PB2_POS1.0 1.9 ND 1.3 ND B-NP-1999-02 11.5 29.2 9.8 19.9 8.2 B-NP-1999-03 23.668.0 13.9 30.4 16.5 B-NP-1999-04 32.1 82.6 8.5 30.8 7.3 B-NP-1999-0511.4 37.0 4.1 17.9 6.1 B-NP-1999-06 27.5 78.1 16.2 37.7 16.2B-NP-1999-08 7.5 36.7 6.8 19.4 7.5 B-NP-1999-10 20.8 61.2 12.7 31.3 14.5B-NP-1999-11 5.9 36.0 6.1 18.4 8.7 B-NP-1999-12 9.7 42.2 7.5 21.4 3.5B-NP-1999-13 32.2 85.2 12.2 37.8 17.5 B-NP-1999-14 14.9 56.6 8.0 5.2 8.5

As a result, out of the 52 double-stranded RNAs, a statisticaldifference was confirmed between 11 double-stranded RNA and the controldouble-stranded RNA against an infection of all virus strains of theabove 5 strains, and those 11 double-stranded RNAs exhibited aremarkable anti-influenza virus activity for any of the virus strainswith a mean S/N ratio of 3 or greater.

On the other hand, PB1-POS, a positive control, exhibited ananti-influenza virus activity for B/Shangdong/07/97 strain andB/Shanghai/361/2002 strain, while it hardly exhibited an anti-influenzavirus activity for other virus strains.

Also, PB2-POS, another positive control, exhibited a very weakanti-influenza virus activity for B/Johannesburg/5/99 strain andB/Shangdong/07/97 strain, and it did not exhibit an anti-influenza virusactivity for other virus strains.

Interestingly, it is to be noted that any one of the antisense strandsof the above 11 double-stranded RNA was RNA having a sequencecomplementary to mRNA of NP protein.

EXAMPLE 4 An Anti-Influenza Virus Activity of Double-Stranded RNA HavingMutation in a Target Sequence

Among the double-stranded RNA which has a remarkable anti-influenzavirus activity for the 5 strains of influenza B viruses found in Example3, homology between B-NP-1999-13 (sequence No. 10) and the nucleotidesequence of mRNA of the 5 virus strains were compared.

The nucleotide sequences registered in GenBank were referred to for the4 strains other than B/Johannesburg/5/99 strain, in which an accessionnumber for each strain was as follows: AY0441698 for B/Shangdong/7/97strain, EF456777 for B/Hong Kong/8/73 strain, AJ784078 forB/Shanghai/361/2002 strain, and AF100359 for B/Victoria/2/87 strain.

As a result, although B-NP-1999-13 had 3 mismatched nucleotides withrespect to B/Hong Kong/8/73, it exhibited a remarkable anti-influenzavirus activity. Also, although it had a mismatch in a second nucleotidecounting from a 5′ end of an antisense strand with respect toB/Victoria/2/87 strain, it similarly exhibited a remarkableanti-influenza virus activity.

Generally, it is said that an RNA interference activity ofdouble-stranded RNA becomes weaker as a mismatch occurs closer to thecenter of a strand from the end and a number of mismatched nucleotideincreases. However, B-NP-1999-13 especially had an RNA interferenceactivity and exhibited a remarkable anti-influenza virus activityregardless of the presence of 3 mismatched nucleotides.

Based on the above results, it was suggested that even a mismatch ispresent, double-stranded RNA having a remarkable anti-influenza virusactivity still exists depending on its nucleotide sequence. Suchdouble-stranded RNA has an anti-influenza virus activity not only forone kind but also for plural kinds of influenza B virus strains,therefore, it was suggested that even in a case when an influenza virusstrain having mutation in a sequence targeted by double-stranded RNAbecomes an epidemic strain, such double-stranded RNA could fully exert atherapeutic effect for an infection caused by the strain.

EXAMPLE 5 A Combinational Use of Double-Stranded RNA Designed to TargetInfluenza a Viruses and Influenza B Viruses

An effect for influenza viruses brought by simultaneous use of aplurality of double-stranded RNA was studied. NP-1496, which was siRNAdescribed in WO2004/028471, was chemically synthesized asdouble-stranded RNA for influenza A viruses. The nucleotide sequence ofNP-1496 is shown in Table 4 with the direction from a 5′ end toward a 3′end. The 3′ ends of sense and antisense strands of NP-1496 have 2deoxythymidine nucleotides attached thereto, and they were denoted inlowercase letters in Table 4. A set of an equal number of moles of theRNA thus synthesized and the antisense RNA thereof was mixed inannealing buffer (i.e., 100 mM KOAc, 2 mM MgOAc, 30 mM HEPES-KOH, pH7.4), followed by denaturation treatment for 5 minutes at 90° C.Subsequently, annealing was carried out by incubation for one hour at37° C., thereby double-stranded RNA was obtained. The above-describedB-NP-1999-13 was used as double-stranded RNA for influenza B viruses.

TABLE 4 Double-stranded Nucleotide sequence of SEQNucleotide sequence of SEQ RNA ID an antisense strand ID Noa sense strand ID No NP-1496 CUCCGAAGAAAUAAGAUCCtt 2475GGAUCUUAUUUCUUCGGAGtt 2476

MDCK cells were suspended in RPMI1640 medium and the suspension wasprepared to have 1×10⁷ cells/mL, to which NP-1496 and B-NP-1999-13 weremixed. To an electroporation cuvette having an interelectrode distanceof 4 mm (product of Shimadzu Corporation), 800 μL of a mixture of theMDCK cells and the double-stranded RNA was transferred. An electricalpulse was applied with voltage of 400 V and a capacitor havingcapacitance of 800 μF by Shimadzu Electro Gene Transfer Equipment(GTE-10), after which the suspension was left to stand for 5 minutes onice. The suspension thus obtained was diluted by RPMI1640 medium to beat 1×10⁶ cells/mL, and FCS was added to make a final concentration of10%. The suspension thus obtained was seeded in a 96-well plate at 0.1mL/well, and cultured for one day at 37° C. in the presence of 5% CO₂.

A/PR/8/34 and B/Johannesburg/5/99 were used as influenza A viruses andinfluenza B viruses, respectively. Each of the viruses was prepared at aconcentration of 1×10⁴ pfu/mL and added at 50 μL/well to the MDCK cellsinto which siRNA had been introduced for virus infection. Afterculturing for 24 hours, the infected cells were fixed with ethanol. Inorder to quantitate viral protein expressed in the infected cells byELISA, the fixed cells were blocked with 10% skim milk, after which ananti-influenza A virus nucleoprotein antibody (product of AbD serotec,MCA400) or an anti-influenza B virus nucleoprotein antibody (product ofAbD serotec, MCA403) was added as a primary antibody. Subsequently, arabbit anti-mouse IgG labeled with HRP (horse radish peroxidase) wasadded as a secondary antibody for recognition of the primary antibody.Then, TMB (i.e., 3,3′,5,5′-tetramethyl-benzidene), which was a substratefor HRP, was added for color development, and absorbance at a wavelengthof 450 nm was measured. An inhibition rate in the wells to which siRNAwas introduced was calculated by the following formula based on valuesobtained from a negative-control well which was not infected withviruses and a positive-control well which was infected with viruseswithout addition of siRNA.

Inhibition rate=(absorbance of a positive-control well−absorbance of asample well)×100/(absorbance of a positive-control well−absorbance of anegative-control well)

The results are shown in FIG. 2. As shown in FIG. 2(A), whenB-NP-1999-13 was solely used at 0.1 nmol/mL, approximately 100% of aninhibitory activity was observed for B/Johannesburg/5/99 viruses. Also,as shown in FIG. 2(B), when NP-1496, which was double-stranded RNA, wassolely used at 1 nmol/mL, approximately 90% of an inhibitory activitywas observed for A/PR/8/34. When a mixture of these double-stranded RNAwas used, an anti-virus activity was exhibited for an infection witheither of the viruses, and the activity level was observed asapproximately the same as when each of the double-stranded RNA was usedsolely.

EXAMPLE 6 A Combinational Use of Double-Stranded RNA Designed to TargetInfluenza B Viruses and Expansion of Spectrum

B-PB2-1999-7 and B-PB1-1999-1, both of which were double-stranded RNA,were used in this test. As for viruses, B/Shanghai/361/2002 andB/Shangdong/07/97 were used. MDCK cells were mixed with thedouble-stranded RNA in a similar manner to Example 5, and introductioninto cell was conducted by electroporation. Each of the influenza Bviruses was allowed to infect after one-day culture, and a combinationaleffect of the double-stranded RNA was measured by quantitating viralprotein present after 18 hours by ELISA using an influenza B virusantibody.

The results were shown in FIG. 3. Although B-PB2-1999-7 exhibitedapproximately 100% of an inhibitory activity for B/Shanghai/361/2002when used at 0.25 nmol/mL as shown in FIG. 3(A), it exhibited as low asapproximately 30% of an inhibitory activity for B/Shangdong/07/97 asshown in FIG. 3(B). Also, although B-PB1-1999-1 exhibited onlyapproximately 20% of an inhibitory activity for B/Shanghai/361/2002 whenused at 0.25 nmol/mL as shown in FIG. 3(A), it exhibited approximately90% of an inhibitory activity for B/Shangdong/07/97 as shown in FIG.3(B). An inhibitory activity as strong as approximately 90% or more wasconfirmed for either of the virus strains, when a mixture of these twokinds of double-stranded RNA was used. As shown above, it wasdemonstrated that there were cases in which no effect was exerted on acertain virus strain depending on a nucleotide sequence ofdouble-stranded RNA, while an effect could be exerted on such a viralstrain by combinational use of a plurality of double-stranded RNA.

EXAMPLE 7 Combinational Effect of Double-Stranded RNA Designed to TargetInfluenza B Viruses

B-NP-1999-3 and B-NP-1999-13, both of which were double-stranded RNA,were used in this test. As for viruses, B/Shanghai/361/2002 andB/Shangdong/07/97 were used. MDCK cells were mixed with thedouble-stranded RNA in a similar manner to Example 5, and introductioninto cell was conducted by electroporation. Each of the influenza Bvirus strains was allowed to infect after one-day culture, and acombinational effect of double-stranded RNA was measured by quantitatingviral protein present after 18 to 30 hours by ELISA using an influenza Bvirus antibody.

The results were shown in FIG. 4. As shown in FIGS. 4(A) and 4(B), thetwo kinds of double-stranded RNA exhibited 80% or more of an inhibitoryactivity for both virus strains either solely or in combination in an18-hour culture. On the other hand, as shown in FIG. 4(C), whenB-NP-1999-3 and B-NP-1999-13 were each used solely at 0.1 nmol/mL and0.05 nmol/mL, respectively, each of them exhibited only approximately10% of an effect for B/Shanghai/361/2002 in 30-hour culture. When amixture of these two kinds of double-stranded RNA was used,approximately 70% of an inhibitory activity was confirmed forB/Shanghai/361/2002. Also, as similarly shown in FIG. 4(D), whenB-NP-1999-3 and B-NP-1999-13 were each used solely at 0.1 nmol/mL and0.05 nmom/mL, respectively, each exhibited 50% and 0% of an inhibitoryeffect for B/Shangdong/07/97, respectively. Meanwhile, when a mixture ofthem was used, 80% of an inhibitory activity was confirmed forB/Shangdong/07/97. As shown above, it was demonstrated that there werecases in which an effect was diminished as culture time of the virus wasextended with use of one kind of double-stranded RNA, however, even insuch a case, the effect was sustained by using a plurality ofdouble-stranded RNA concurrently.

1. A double-stranded RNA which inhibits replication of influenza Bviruses by RNA interference, wherein the double-stranded RNA comprisesan RNA having 19 to 25 nucleotides homologous with a part of an mRNAtranscribed from a genomic RNA of the influenza B viruses and anantisense RNA thereof.
 2. The double-stranded RNA according to claim 1,wherein the mRNA is an mRNA of an NP protein gene, an RNA polymerase PAsubunit gene, an RNA polymerase PB1 subunit gene, or an RNA polymerasePB2 subunit gene.
 3. The double-stranded RNA according to claim 1,wherein the RNA is selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or selectedfrom the group consisting of RNA of nucleotide sequences as set forth inSEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted. 4.The double-stranded RNA according to claim 1, wherein the RNA isselected from the group consisting of RNA of nucleotide sequences as setforth in SEQ ID NOs: 1 to 11 or selected from the group consisting ofRNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 11 in which1 to 3 nucleotide(s) is/are substituted.
 5. The double-stranded RNAaccording to claim 1, which has a S/N ratio of 3 or greater in screeningof double-stranded RNA by a transfection microarray usingB/Johannesburg/5/99 strain.
 6. The double-stranded RNA according toclaim 1, wherein the RNA optionally contains one or more modifiedribonucleotide(s).
 7. The double-stranded RNA according to claim 1,wherein one or more phosphodiester bond(s) in the RNA is/are optionallysubstituted with phosphorothioate bond(s).
 8. The double-stranded RNAaccording to claim 1, which forms blunt ends.
 9. A double-stranded RNAhaving DNA or RNA of 1 to 4 nucleotide(s) attached to 3′ ends of thesense and the antisense strands of a double-stranded RNA according toclaim 1 to form overhanging ends.
 10. A hairpin RNA which forms thedouble-stranded RNA according to claim 1 in a cell, wherein the RNAhomologous with a part of an mRNA transcribed from a genomic RNA of theinfluenza B viruses is linked to an antisense RNA thereof by a linkersequence.
 11. An expression vector for a double-stranded RNA whichcomprises a first DNA complimentary to an RNA selected from the groupconsisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1to 57 or an RNA selected from the group consisting of RNA of nucleotidesequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3nucleotide(s) is/are substituted and a second DNA complimentary to thefirst DNA, as well as promoters on 5′ sides of each of the first DNA andthe second DNA, wherein, in a cell to which the vector is introduced,the vector transcribes a first RNA complimentary to the first DNA and asecond RNA complimentary to the second DNA, and the first RNA and thesecond RNA hybridize to each other to form a double-stranded RNA.
 12. Anexpression vector for a double-stranded RNA which comprises a first DNAcomplimentary to an RNA selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an RNAselected from the group consisting of RNA of nucleotide sequences as setforth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/aresubstituted, wherein the RNA has an RNA having 1 to 4 nucleotide(s)attached to 3′ ends thereof, and a second DNA complimentary to an RNAwhich is antisense RNA of an RNA selected from the group consisting ofRNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or anantisense RNA of an RNA selected from the group consisting of RNA ofnucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3nucleotide(s) is/are substituted, wherein the RNA has an RNA having 1 to4 nucleotide(s) attached to 3′ ends thereof, as well as promoters on 5′sides of each of the first DNA and the second DNA, wherein, in a cell towhich the vector is introduced, the vector transcribes a first RNAcomplimentary to the first DNA and a second RNA complimentary to thesecond DNA, and the first RNA and the second RNA hybridize to each otherto form a double-stranded RNA.
 13. An expression vector for a hairpinRNA which comprises DNA strands encoding a hairpin RNA, in which anantisense DNA complimentary to an RNA selected from the group consistingof RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or anantisense DNA complimentary to an RNA selected from the group consistingof RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 inwhich 1 to 3 nucleotide(s) is/are substituted is linked to a DNAcomplimentary to the antisense DNA by a linker sequence, as well aspromoters on 5′ sides of the DNA strands, wherein, inside the cell towhich the vector is introduced, the vector transcribes the hairpin RNA,and the hairpin RNA is processed in a cell to form a double-strandedRNA.
 14. A pharmaceutical composition which comprises at least one kindof a double-stranded RNA according to claim 1 as an active ingredientand one or more pharmaceutical additives.
 15. (canceled)
 16. A detectionkit for influenza B viruses which comprises at least one of adouble-stranded RNA according to claim 1 and a transfection reagent. 17.The pharmaceutical composition according to claim 14, which furthercomprises a double-stranded RNA which inhibits replication of influenzaA viruses by RNA interference.
 18. (canceled)
 19. A method for treatmentof an infectious disease caused by influenza comprising administering toa patient in need thereof at least one kind of a double-stranded RNAaccording to claim 1 as an active ingredient.
 20. The method fortreatment of an infectious disease caused by influenza according toclaim 19, which further comprises administering to the patient adouble-stranded RNA which inhibits replication of influenza A viruses byRNA interference.